Same-Day Positron Emission Tomography/Computed Tomography with ⁶⁸ Ga-Radiolabeled Fibroblast Activation Protein Inhibitors and ¹⁸ F-Fluorodeoxyglucose Imaging for Gastrointestinal Cancers

<b><i>Objective:</i></b> We investigated the clinical practicability of same-day ⁶⁸Ga-radiolabeled fibroblast activation protein inhibitors (⁶⁸Ga-FAPI)-first and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) imaging and compared it with same-day ¹⁸F-FDG-first or 2-day procedures in diagnosing gastrointestinal cancers. <b><i>Materials and Methods:</i></b> Sixty-five patients with confirmed gastrointestinal cancers were divided into same-day ⁶⁸Ga-FAPI-first group (Group A), same-day ¹⁸F-FDG-first group (Group B), and 2-day group (Group C). Low-dose CT and low injection activity were performed on ⁶⁸Ga-FAPI positron emission tomography/computed tomography (PET/CT). Interval times, radiation dose, diagnostic performance, and detectability were assessed among groups. Additionally, the uptake, tumor-to-liver ratio (TLR), diagnostic efficacy, and TNM stage were compared between the two modalities. <b><i>Results:</i></b> The total waiting time for Group C was significantly longer than that for Group A or B (both <i>p</i> < 0.001). The total dose-length product and effective dose decreased in all groups. There were comparable detectability and diagnostic performance among groups (all <i>p</i> > 0.05). The within-group analysis in Group B indicated that ⁶⁸Ga-FAPI PET/CT had higher uptake in the primary and recurrent lesions than ¹⁸F-FDG without differences in TLR, due to higher liver background on ⁶⁸Ga-FAPI PET than Group A or C (both <i>p</i> < 0.001).⁶⁸Ga-FAPI PET/CT possessed higher accuracy than ¹⁸F-FDG and changed staging in 14 patients (14/65, 21.54%). <b><i>Conclusions:</i></b> The same-day ⁶⁸Ga-FAPI-first and ¹⁸F-FDG imaging reduced examination waiting time without increased radiation dose, simultaneously achieving excellent diagnostic performance and improving clinical staging in diagnosing gastrointestinal cancers.